European Patent No. 158,354 describes a keyless access system for motor vehicles having a portable transceiver. Authorization of a user to gain access and to drive a vehicle is verified on the basis of a signal emitted by the transceiver. If locking is desired, the user is notified by an alarm signal indicating that the transceiver is still in the interior of the vehicle in order to avoid lock-in of the transceiver. Final locking of the vehicle, however, is performed only after a certain period of time has elapsed to allow the user an opportunity to retrieve the transceiver from the interior of the vehicle within this period of time. If the user fails to do so, the vehicle is locked and the transceiver inside the vehicle is deactivated. Renewed access to the interior of the vehicle is only possible in combination with a mechanical vehicle key.
If a user does not react promptly to the warning signal transmitted, a great deal of effort is required to gain access to the vehicle again.